Prior to this commit, it was not possible to test Rocket crates in
production mode without setting a global secret key or bypassing secret
key checking - the testing script did the latter. The consequence is
that it became impossible to test secret key related failures because
the tests passed regardless.
This commit undoes this. As a consequence, all tests are now aware of
the difference between debug and release configurations, the latter of
which validates 'secret_key' by default. New 'Client::debug()' and
'Client::debug_with()' simplify creating an instance of 'Client' with
configuration in debug mode to avoid undesired test failures.
The summary of changes in this commit are:
* Config 'secret_key' success and failure are now tested.
* 'secret_key' validation was moved to pre-launch from 'Config:from()'.
* 'Config::from()' only extracts the config.
* Added 'Config::try_from()' for non-panicking extraction.
* 'Config' now knows the profile it was extracted from.
* The 'Config' provider sets a profile of 'Config.profile'.
* 'Rocket', 'Client', 'Fairings', implement 'Debug'.
* 'fairing::Info' implements 'Copy', 'Clone'.
* 'Fairings' keeps track of, logs attach fairings.
* 'Rocket::reconfigure()' was added to allow modifying a config.
Internally, the testing script was refactored to properly test the
codebase with the new changes. In particular, it no longer sets a rustc
'cfg' to avoid secret-key checking.
Resolves#1543.
Fixes#1564.
